Electric load limiter



y 5, 1953 E. F. KINGSLEY 2,637,822

ELECTRIC LOAD LIMITER Filed July 29, 1950 IE j 0% INVENT0R.. Errol E Kiqgsley wzzw H sggen 2 Patented May 5, 1953 ELECTRIC LOAD LIMITER Errol F. Kingsley, Portland, reg., assignor to Iron Fireman Manufacturing Company, Portland, Oreg.

Application July 29, 1950, Serial No. 176,618

14 Claims.

This invention pertains to electric load limiters, and relates particularly to the novel construction of a device by which auxiliary loads are removed from an electrical circuit automatically and in sequence as the addition of primary loads reaches an established maximum capacity for the circuit.

It is a principal object of the present invention to provide an electric load limiter which accommodates ready adjustment to any desired maximum circuit capacity, whereby to afford with but one limiter device the accurate and positive control of circuits having diverse load characteristics.

Another important object of this invention is the provision of an electric load limiter which accommodates the control of each of a plurality of auxiliary loads by a sequence determined by the said auxiliary loads, whereby only selected auxiliary loads are removed as required.

A further object of this invention is the provision of an electric load limiter of simplified and economical construction and which is adaptable to circuits of various load characteristics merely by the selective exchange of a coupling element forming a part of the limiter device.

These and other objects and advantages of the present invention will appear from the following detailed description taken in connection with the accompanying drawing, in which: l

Figure 1 is a diagrammatic view of an electric load limiter embodying thefeatures of-this invention and showing the same in operation in a circuit having a plurality of primaryand secondary loads;

Figure 2 is a diagrammatic view similar to Figure 1 showing a modified form of electric load limiter embodying the features of the present invention; and V Figure 3 is a diagrammatic view of a modifie form of coupling means.

- Stated broadly, the load limiter of this invention comprises a pair of cooperating relay coils for each auxiliary load, one of which coils'is arranged in parallel with a coupling elemen disposed in series in the main circuit.

Referring to the drawing, the main power is supplied by source I through the distributing lines 2 and 3 to the primary loads indicated collectively at 4. By primary loads is meant those electrical devices which are considered important to maintain in continuous operation. In a factory these loads may comprise the essential operating equipment, the lighting system and other devices the functioning of which-is important to constant production. In the home these primary loads may comprise the lighting system, the refrigerator, stove and other devices whose availability for immediate and uninterrupted service are considered important.

A plurality of auxiliary loads 5, 6, l and 8 are shown in the drawing to be arranged in parallel with each other and with the primary load 4. In a factory, for example, auxiliary loads may comprise those devices Whose functions do not contribute essentially to the continued operation of the plant. In the home, auxiliary loads may comprise electric space heating elements, the water heater and other devices whose services may be discontinued temporarily when necessary.

In the circuit of auxiliary load 5 is a switch shown as comprising a pair of normally closed contacts 9. The movement of these contacts between the closed and open positions is controlled by the energization and deactivation,respectively, of relay coil 10. One end of coil 10 is connected to the main line 2, while the opposite end thereof is connected through the normally open contacts H to main line 3. The operation of contacts H is controlled by relay coil I2.

Relay coil [2 is connected at one end to line 3 at one end of the coupling resistor l3 disposed in series in the said line. The opposite end of coil 12 is connected through rectifier I 4 to the opposite end of resistor I3. 'Theresistor is preferably arranged for detachable'connection in line 3 in such manner that it removal will break the electrical circuit to the coil l2. Condenser I5 is placed in shunt withcoil I2at the output of rectifier M to smooth out the rectified current, in manner well-known in the art.

Referring to the drawing, it is apparent that each auxiliary load is provided'with a control systemas described With'reference to load 5. Thus, load 6 is connected to the lines 2, 3 through contacts which are actuated by the system comprisin relay coil l contacts 8 and relay coil [9. The activation of coil I9 is controlled by contacts 20, as explained in detail hereinafter. In similarmanner, load 1 is controlled by contacts 2|, relay coil 22, contacts 23, relay coil 24 and contacts 25, while load 8 is controlled by contacts 26, relay coil 21,"contacts 28, relay coil 29 and contacts 3D.

It is to be noted that the series combinations of relay coils' l0, l1, 22and 21 and the respective contacts I I, I8, 23 and 28 are arranged in parallel with each otherand connected tothe lines 2, 3, as previously mentioned.v It will .be apparent from the following discussion that these coils l0,

3 ll, 22 and 21 may be operated from a source of potential other than the source l.

t is to be noted further that the series combinations of relay coils I9, 24 and 29 and the respective contacts fill, 25 and to are arranged in parallel with each other and with relay coil l2, across the resistor i3.

In the embodiment illustrated in Figure l of the drawing, contacts 2%, 25 and 3d are actuated by relay coils iii, ll and 22, respectively. Thus, when coil I2 is energized by virtue of an excessive load current being impressed across resistor l3, cone tacts H are closed to energize coil l8, whereupon contacts 9 are drawn open to'remove theauxiliary load 5 from the main circuit and contacts 20 are drawn closed to complete the circuit to relay coil 19. It is to be observed, however, that contacts 9 move only a short distance to effect breaking the circuit to load 5 as compared to the longer distance of travel of contacts as in completing the circuit to coil it, Thus, load 5 is removed before coil [9 is energized and, in the event thatremo-val of load 5 is sufficient to reduce the total load urrent ss esis o l3 belew the sta h d maximum, current is not available to energize coil I9 sufficiently-to close contacts l8, In this manner, successive auxiliary loads are not caused to be rerloved for the instant which would otherwise occur if the foregoing delay were not. provided.

In the modification shown in Figure 2, contacts 2t, 25 and so are actuated by relay coils l2, l5 and 2d, respectively. In this arrangement the energization of coil 82 upon the occasion of an over-load on the main circuit eiiects the closing of contacts H and 2&3. In order to avoid substantially simultaneous ener-gization of coils l and i2, and therefore simultaneousenergization of the succeeding similar pairs of'coils, it is desire able to delay the closing of contacts 29, 25 and 3t until their complementary contacts H. l8 and 23 have closed. In this manner the relay coils U2, i a 2 may op r e to. op n h r spe v contac i f; an 2! and e cve e leads 6 and l in successive order before the coils I2, is it ec e energizedi s fo example, as coil is energized contacts H close to energize coil to and open contacts 9, Load 5 is'thereby removed from the main circuit before contacts 29 ec m c s d: n h e e t as ex aine h re inbefcre, that removal of load 5 reduces the total current across resistor 13 below the established max mum coil wi l not bec meene sizee...

i s met ods n means er delayin the. cl sin and Qu ui e ec i a ntacts are 1 known to those skilled in the art:- The mechanis cal dash pots shown SQhematically in the drawing are intended merely to illustrate the function of the delay. Since the type of delay mechanism does not form a part or" the present invention, further description thereof is not presented.

The delay mechanism represented schematically in Figure 2 by the dash pots 3'! connecting the movable contact of each pair of contacts 2%, 25 and (it need only be of the'type which accommodates delay in closing the contacts. llhis is p a n f r t r s n t t wh n t e tota load current across resistor it drops below the established maxim-11m, all of thecoils l2, i9, 293. and 29 become deeneriZ6d re ardless of the position of the contacts 211, 25 and 30,. Delay in the 0105-. ing of said contacts, however, permit their com-v plementary contacts H, H} and 23,. respectively, to close first andthereby remove an. auxiliary 4 load before possible activation of the next succeeding coil.

The delay mechanism represented schematically in Figures 1 and 2 by the dash pots 32 connecting the movable contact of each pair of contacts H, M, 23 and. 23 is of the type which accommodates delay in opening the contacts, and preferably of the type in which the time delay is capable of being adjusted. The time interval of delay in opening the contacts thus may be decreased progressively from relay coil 29 through relay 6011s 24 and 59 to coil l2. In this manner, as explained in detail hereinafter. when said coils have been d'eenergized by reduction of the total load current sufiiciently below the established maximum, contacts 28 will open first to deenergize coil 27 and restore load 8 to the circuit. Contacts 23 will then open to restore load 7 to the circuit, following which contacts It will open to restore load 6 to the circuit. Finally contacts H open and load cisrestored tothe circuit. This arrangement is particularly desirable in order to prevent a sudden restoration of all auxiliary loads to thecircuit, as explained in detail hereinafter.

It will be apparent to those skilled in the art that the progressive time delays of dash pots 32 may be arranged with respect to the various auxiliary loads in any pattern desired. Thus,. for example, it may be desired to restore the loads in the time sequence 5, 6, 7, 8, 0rd 8, 7, 5, or in any other predetermined order. This merely requires the judicious selection of time delays.

For purposes or the following description of the operation of the present invention, let it be as s nned that the value of resistor I3 is chosen to supply sufficient current to coils i2, i9, 2d and-29 to actuate the cooperating contacts when the power impressed on lines 2, 3 exceeds 10 kilos watts. Assume further that auxiliary loads 5, 6, i and 8 are on the lines and re resent 2 kilowatts each; while the primary load l on the lines represents 2 kilowatts. The 10 kilowatts of power thus being used is insufficient to operate the relay coils.

Assume now that an additional primary load of 3 kilowatts is placed on the lines. The 13 kilowatts of power thus impressed causes activation of rela coil !2. Referring to Figure l of the drawing, the energization of coil 12' results in the closing of contacts H and the energization of coil it. Contacts l open immediately to removethe. 2- kilowatt load 5 from the lines, there by reducing the total load to 1.1 kilowatts. Con tacts 20' close. to energizerelay coil l9, where.- upon contacts it close and coil l'lbecomes, activated. Contacts 56 are immediately opened to remove the 2 kilowatt load 6 from the lines and thus reduce the total load to 9 kilowatts. Contacts 25 also close, but the 9 kilowatts; total load is insufiicient to energize coil 2%.

Let it be assumed further that coils i2, 19, 2e and 29 are'of, the well known type. inv which deactivation occurs; only. when the current is reduced, for example, to a value below per centv of the current required for energization. Thus, the coils are not deenergized'until the totalload on lines 2, 3 drops below Skilowatts. Since the removal of auxiliary loads 5 and- 8 reduced the total load to. 9 kilowatts, the system will-remain at that load level for proper operation.

Assume-now that an additional primary load of 4 kilowatts is. placed on the-lines, increasing the total to l3 kilowatts. Since contacts 2-5, have previously been closed, coil 24. now becomes. energized. Contacts 213' are thus closed, coil 22.

is energizedand-contacts .21 :ap'en: to :removthe 2 kilowatt auxiliary load-Iifrom the circuitand reduce the total load to 11 kilowatts. Contacts 30 close to energize coil 29 and 'closec-onta'cts 28, whereupon coil 2'! is energized and Contacts 26 open. Removal of 'the 2 kilowatt load 8 reduces the total load on lines 2, 3 to 9 kilowatts.

The operation of the system shown in Figure 2 in accordance with the foregoing example is'substa'ntially the same as "in Figure l'with the exception that the inherent time delay between the opening of contacts9, I6 and 2I and the closing of contacts 26, 25 and 30, respectively, in Figure 1 is achieved in Figure 2 mechanically by the delay mechanisms 31 provided on contacts 20, 25 and 30.

Assume now that f1 kilowatts of-primary load is removedfrom the circuit,- reducing the total load to kilowatts- Since the total load has been reduced below the value at which relay coils I2, I9, 24 and 29 become deenergized, their respective contacts II, I8, 23 and 28 are free to open. In the event that the delay mechanism 32 is not employed, the said contacts open simultaneously to place'auxiliary loads 5,; '6, I- and 3 contacts 28 open first and auxiliary load 8 isreinstated in the main circuit. The totalload increases to '7 kilowatts. Contacts 23 open next to replace load I in the circuitand-increase the" total load to 9 kilowatts. Since-contacts II and I8 are still closed, coils 'Is and I2 are now 'affected by 9 kilowatts of load and, since they release only after the load is reduced to below 8 kilowatts, the contacts [8 and I I do not open. Thus, the provision of progressive delay obviates the hunting for proper load level as is necessarily experienced in the systems having nomeans for delay.- Y

It will be apparent to those skilled in the art that atransformer may be substituted for or employed in conjunction with the resistor I3 with I out departing from the scope and spirit of the present invention. I r

A further modification may be made for use in a three wire circuitwhereinfthe total load is distributed between the said lines.- Referring to Figure 3 of the drawing, there is shown the three supply lines '33, 34 and 35. In many instances the loads impressed, for 'example, across the lines 33 and 34' may be substantially different in magnitude from the -loa'd'on lines 34 and 35. It is desirable to impress upon the relays I2, I9, 24 and 29 the effects of the total load operating in the circuit, and thereby obtain most efficient control. This may be accomplished in the manner illustrated in Figure "3, wherein resistors 36 and 31 are placed in-series in-lines 33 and'35, respectively. Transformer windings 38 and 39 are placed in shunt with the respective resistors 36 and 31, and coupled to the common winding 46. The latter is .connectedin shunt with the parallel-relays I2, I9, 24 and '29, in the manner 'of'r'esisto'r I3 as explainedh'erein-i before. The'rectifier I4 andcondenser. I5 may be employed if desired; In theforegoing .manner, the reflects-of". the :loads. impressed. across 8. bothireslstors 36aand 3Ijis impressed upon trans former winding ..-40,'..whereby the parallel relays respond to the CiIbllitJ It is apparent that'the coils 38 and 39,may betus'ed alone, he. without parallel combination with their respective resistors 36 and 31.. Since, in any case, the function of the element.

In the drawing and'foregoing description the coils I2, I9, 24 and 29 are shown to be of the type operated by direct current. It is apparent' that relay coils'of the alternating current type may also be'employed, in which case the rectifier I4 and condenser I5 may be eliminated. As stated h'ereinbefore, the coils' I0, I1, 22 and 21'may be connected to a source of potential independent from source I because their operation is not dependent directly upon the characteristics of the load on lines 2, 3.

It is apparent further that any number of auxiliary loads may be controlled merely by providing additional relay coils and contacts for each load to be controlled, in-th'e manner previously described. An auxiliary load may include a plurality of electrical elements operated ona single circuit, as is well-known in the art.

The foregoing and other modifications and changes may bemade in the present invention without departing from the scope and spirit thereof. It is to be understood, therefore, that the foregoing description merely illustrates the features of theinvention' and is not defining the limits thereof.

From the foregoing description it means for controlling the load impressed upon an electrical circuit. The provision of a removable coupling resistor, either alone or in combination: with a transformer, affords utility of the device in circuits of difierent or variable load charac teristics, thereby obviating the former necessity of providing a plurality'of limiter devices each constructed to accommodate a specific circuit. The arrangement of a pair of relays for each auxiliary load circuit prevents arcing between the contact points of the normally closed switch in' the circuit by virtue of the positive activation and deactivation of the cooperating relay by the operation of the normally open switch and second relay. The parallel arrangement of relay and switch units accommodates the control of any number of auxiliary loads and in any sequence of operation, thereby permitting arrangement of loads sequentially in the order of their relative importance. The load limiter is of simplified and, therefore, economical construction, the provision of a minimum of moving parts enhancing considerably the life and consistency of ing the normally. .open switch .meanspand cou-.

effects .of the total load on. the

the appended claims as couintended as j v I I v is apparentthat the present invention provides versatile accents? pitta means connecting. the second relay means in" series the said electricalcircuit.-

2 In combination with an. electricalcircuit including a plurality of auxiliary loads, normally.

closed-switch means. in. each. of the auxiliary load: circuits, a plurality of relay means, each re-- lay means actuating: one of: the manually closed? switch means, normally open switch means-lathe circuit of-eaohz-relay means, a plurality of sec ond' relay means. cachactuating one'of the normally open switch means, second; normally open switch means in the circuit of each at the sec 0nd; relay means succeeding-the first in order,

coupling meansconnecting' the seconct relay means in series in the saidelectr'ical circuit;

3t Imcombinati'on witlr an electrical circuit including. a plurality oi. auxiliary loads, normally closed) switch means in eaclrof the auxiliary load; circuits, a plurality of relayzmeans, each ro lay means-actuating, one of thenormally closed switch means, normally open-switch means the circuit-of each. relay'means, a plurality of sec ond relaymeans connected. in parallel, each ac nected. in-para-ll'el to said electrical. circuit, each relay means-actuating. one ot the normally closed switch mocha-normally open switch means in the circuit of each relay means, a plurality of second relay means connected in. parallel, each actuating one-0t the normally opert switch means, secondnormally open. switch. means in the'circult of each of the second relay meanssuccee'di-ng the first in order, and, coupling. means,: connecting the parallel secori'direlay means in series in the saidelectrical circuit.-

5; In combination with. an. electrical circuit including a pluralityof. auxiliary loads. normally closed switch means in each of the auxiliary load circuits, a. plurality ofv relay means, each i e-- lay means actuating. one or the normally closed switch means, normally open. switch means in the circuit of each relay means," a plurality of secondixrelay means each. actuating one .of the normally open switch means, anormally closed switc'll means, a-fi-rs't relay means: a first normally open switch means and. a second; relay means com-prising a unit, second normally open. switch means in. the circuit of'each of the second relay means succeeding the first inorder, each of the second. switch. means being actuated by one of the relay means of the next preceding unit, and cou ling means connectin the second relay means in series in the said electrical circult;

6. In combination with an electrical circuit including a plurality or auxiliary loads, normall closed switchmeans: in each of the auxiliary load 'circuitsga plurality oi relay means; each relay means actuating one of the normally closed means, normally openswitch means in tl re'circui t of each relay rliear is, ap'lura-l ity ofs'ec'onn relay means each actuating one or the normally o en switch means, anormail closeds'witcrr means, a" first relay means; a first nor-- many open switch means anoa secon'clrel'ay meanscomprising a unit, secondi'normally' o en switch meansk'imthc circuit of each or the. sa emonetary-"means succeeding theyfirst in order, each of-the second. switch means beingactivated by me first r'elaymeanstof the: next preceding. unit, and coupling:.means connec-ting;thesecond' relay me'ans series the saidelect-rical-circhit.-

l'; In combin-ationwitlr an electricalcircuit ineluding a plurality 0t auxiliary loads, normally closed switch means each ot the auxiliary load circuits, a: plurality-of relay means, each relay means actuating one of the normally closed switch means, normall y opeir switch means in the.- circuit of relay means; a plurality of second: relaymeans each actuating, ono. of the. normally open switch means, a normally closed switch means, afirst'r'elay' means, a first normally open switchv means: and a; second relay means comprising. a unit, ,secononormally open switch means in the-circuit of eoch otthese'cond relay means. succeedingtho'first in ordergeach or the secondswitch means being actuatedhy the secone relay means of the next preceding unit, andcoupling, means connecting; the second relay means in series in. thesaio electrical circuit 8. in combination with an electrical circuit in-- eluding amplur'alityof auxiliary loads, normally closed: switch means inj each of. the auxiliary load ci-rc'uitsy a plurality or relay means, each relay means actuating one of the normally closed; switch means; normally opal-switch meansim the circuit or each relay means a plurality of. second relay means each -ac-tuatinri.v onerof the normally open switch means, .anormally closed switchmeans, a first relay means afirst normally open switch means and-a second relay meansv comprising a unit, second normally open switch means in the circuit oi each of the second relay meanssucceedingthe first in order,- coupling means connecting the-second: relay means in. series in the said electrical circuit, and delay means on. the first norm-ally open switch means ofeach unit for controlling the sequence of openingv of said switch means- 9-. In; combination with an. electrical. circuitiineludingv a plurality of auxiliary loads, normally closed switch means in each of the auxiliary loaol circuits, a plurality of relay means, each relay means actuating one off the normally. closed switch means, norm-ally open switch means in the ircuit of each relay means, a plurality of second.

relay means each actuating one oi the normally.

open switch means, a normally. closed; switch means; afirstrelay means,, a first normally open switch means. and a secondv relay means conr-. prising a; unit, seconds normally open switch means in the circuit of each. oi thesecond relay.

means succeeding the first in order, coupling means connecting second relay means in series inthe-said; electrical circuit, and delay means on the second normally open switch means for delaying the-closing thereof relative to the; closing. of the first normally openv switch means of. the next pr'ececlir'rgv unit.v

lO.- In combination with an electrical circuitincluding aplurality of auxiliary loads,I normally. closed switch means in each ofthe auxiliary loacl. circuits, a plurality of relaymeans, each relay means actuating; one of the normally closedswitch means, normally open switch means in the circuit oi eaclrrelay-means, a plurality of second relay means each actuating one of the normally openswitclzr means, a normally closed switch means.,afirst relay means, a first normal 1y open swltch'means and a: second-relay means:

comprising a unit, second normally open switch means in the circuit of each of the second relay means succeeding the first in order, coupling means connecting the second relay means in series in the said electrical circuit, delay means on the second normally open switch means for delaying the closing thereof relative to the closing of the first normally open switch means of the next preceding unit, and delay means on the first normally open switch means of each unit for controlling the sequence of opening of said switch means.

11. In combination with an electrical circuit including a plurality of auxiliary loads, normally closed switch means in each of the auxiliary load circuits, a plurality of relay means, each relay means actuating one of the normally closed switch means, normally open switch means in the circuit of each relay means, a plurality of second relay means each actuating one of the normally open switch means, a normally closed switch means, a first relay means, a first normally open switch means and a second relay -mea-ns comprising a unit, second normally open switch means in the circuit of each of the second relay means succeeding the first in order, each of the second switch means being actuated by the first relay means of the next preceding unit, coupling means connecting the second relay means in series in the said electrical circuit, and delay means on the first normally open switch means of each unit for controlling the sequence of opening of said switch means.

12. In combination with an electrical circuit including a plurality of auxiliary loads, normally closed switch means in each of the auxiliary load circuits, a plurality of relay means, each relay means actuating one of the normally closed switch means, normally open switch means in the circuit of each relay means, a plurality of second relay means each actuating one of the normally open switch means, a normally closed switch means, a first relay means, a first normally open switch means and a second relay means comprising a unit, second normally open switch means in the circuit of each of the second relay means succeeding the first in order, each of the second switch means being actuated by the second relay means of the next preceding unit, coupling means connecting the second relay means in series in the said electrical circuit, and delay means on the second normally open switch means for delaying the closing thereof relative to the closing of the first normally open switch means of the next preceding unit.

13. In combination with an electrical circuit including a plurality of auxiliary loads, normally closed switch means in each of the auxiliary load circuits, a plurality of relay means, each relay means actuating one of the normally closed switch means, normally open switch means in the circuit of each relay means, a plurality of second relay means each actuating one of the normally open switch means, a normally closed switch means, a first relay means, a first normally open switch means and a second relay means comprising a unit, second normally open switch means in the circuit of each of the second relay means succeeding the first in order, each of the second switch means being actuated by the second means of the next preceding unit, coupling means connecting the second relay means in series in the said electrical circuit, delay means on the second normally open switch means for delaying the closing thereof relative to the closing of the first normally open switchmeans of the next preceding unit, and delay means on the first normally open switch means of each unit for controlling the sequence of opening of said switch means.

14. In combination with an electrical circuit including a plurality of auxiliary loads, normally closed switch means in each of the auxiliary load circuits, a plurality of relay means, each relay means actuating one of the normally closed switch means, normally open switch means in the circuit of each relay means, a plurality of second relay means each actuating one of the normally open switch means, second switch means in the circuit of each of the second relay means succeeding the first in order and actuated by one of the relays controlling the next preceding auxiliary load, and coupling means connecting the second relay means in series in the said electrical circuit.

ERROL F. KINGSLEY.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,194,165 Fry Aug. 8, 1916 2,480,452 Dole Aug. 30, 1949 

